GM Service Manual Online
For 1990-2009 cars only

Metric wheel/nuts and bolts are identified in the following way:

    â€¢ The wheel/nut has the word Metric stamped on the face.
    â€¢ The letter M is stamped on the end of the wheel bolt.

The thread sizes of metric wheel/nuts and the bolts are indicated by the following example: M12 x 1.5.

    â€¢ M = Metric
    â€¢ 12 = Diameter in millimeters
    â€¢ 1.5 = Millimeters gap per thread